What am I looking at? Fossil? Old bones? Animal? Plant? Sea creature?

August 7

Hello!

I inherited someone’s rock collection and this sandstone rock was in it. It has a cast of what looks to be some type of tunnel system and then it has a small fan like animal/plant “trace” about 4cm. I thought at first it was a fossil, but after looking at it under some microscopes I’m not positive now. I don’t actually know what a fossil this small looks like under a microscope (20x-100x).

I unfortunately have no idea where this rock came from so I don’t expect an exact species, but if someone could tell me if it is a fossil or just old bones and what category it could be (plant, animal, bug, sea creature, etc.) that would be helpful! As far as I can tell there are three “branches” and a “fan” matrix on both sides, however the right side is mostly eroded away. The left side is mostly intact and it looks to have a spot with something on it. I thought this was just a piece of rock still stuck to it, but after looking under the microscope it’s definitely made of the same material as the rest of the structure. However, the spot looks like it’s darker in color. It also has an interesting “stem” or “head” area that after looking at it for so long has started to look like a pirate’s skull lol so I’ve dubbed it the “pirate’s head”. Anyways, I focused on the branches, left fan, and pirate’s head in the close ups and tried to get the best contrast possible. I also included some very up close looks any the pirate’s head so you can better tell what the mineral structure looks like. Sorry about all the photos, I figured as much documentation of it would be in determining at least what type of life form this was.

Thank you in advance for whatever help you can give me!

-Kalei

cast tunnel?